Carburetor



23, 1958 D. D. STOLTMAN I 2,821,371

CARBURETOR Filed June 25, 1956 LI [I if .10

if I y 1 26 z P i! 56 z r7 2 L Y yo INVENTOR. 50 W 72414 a sw m HIS ATTORNEY United States Patent CARBURETOR Donald D. Stoltman, Rochester, N. Y., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application June 25, 1956, Serial No. 593,612

7 Claims. (Cl. 261-43) This invention relates to carburetors for internal combustion engines and particularly to compound carburetors having primary and secondary mixture passages, which become effective sequentially, the primary mixture passages being effective at all operating speeds, while the secondary mixture passage or passages become effective only 'at relatively high speeds.

Compound carburetors are geneerally dual in character or have four mixture passages. In the dual type there is one primary mixture passage and one secondary mixture passage each controlled by a single throttle which is generally manually operated. In the type which has four mixture passages, there are two primary passages and two secondary, the primary passages being controlled by two primary throttles on a common shaft and the secondary passages being controlled by two secondary throttles, also on a common shaft. The primary throttle shaft is generally operated manually by an operating connection extending directly to the conventional accelerator pedal and the secondary throttle shaft is usually operated through some form of lost motion connection which does not become elfective with respect to the secondary throttle shaft until the primary throttle or throttles is or are opened to a predetermined extent, for example 40. The mechanism is so constructed that the secondary throttle shaft is given its complete movement during the balance of the movement of the primary shaft required to bring the primary throttle or throttles to full open position.

It has sometimes been observed in connection with compound carburetors that when the engine is operating at relatively low speed, with secondary throttle or throttles closed, and the throttle operating mechanism is moved enough to move both primary and secondary throttles to a relatively wide open position, the combined primary and secondary air flow passage is too large and the nozzle suction is too low for proper fuel metering. To avoid this difficulty, it has been customary in some instances to provide an unblanced suction-operated valve in the secondary mixture passage, or such a valve in each of the secondary passages if there are more than one. Such a valve was, of course, opened by the flow of air and suitable means, such as a spring or a weight, have been provided to retard the opening movement of such valve. I

Generally, in devices of this character, the means which retards the opening of the suction operated valve is so constructed that it presents approximately the same, or an increasing, force of opposition to the opening of the valveas the valve is progressively opened when the suction thereon is progressively increased, as the throttle valves are opened. As the suction operated valve opens, the suction decreases, and if the force retarding opening increases or remains the same as the valve opens, a given increase in suction would produce less and less movement of thesuction operated valve or valves as the throttle valves were opened and, hence,the suction operated I "ice valves will either begin to open at too low a suction or would never fully open due to inadequate suction.

It is the primary purpose of this invention to provide suction-operated secondary air valves of the character described and means to oppose the opening of such valves which is so constructed that the opposing force exerted by such means to the opening of the valve varies, in approximately the same way as the suction which is effective on the valve varies for any given change in suction anterior to the throttle valve or valves. In other words, it is the principal object of the invention to provide means which retard the movement of the secondary suction-operated valves with a decreasing force as the suction valves open. Thus, the suction operated valves will open fully relatively fast and will remain fully open over a wide range of engine speed as caused by variation in engine load with the primary and secondary throttles wide open.

According to the present invention, this purpose is achieved by providing a spring which opposes the opening movement of the secondary air valves through a variable torque or lever arm so that the leverage through the medium of which the spring operates to oppose the opening of the secondary valve or valves progressively decreases as the valve or valves move toward open position.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

Fig. l is a side elevation of a four outlet carburetor, partly in section, in which the present invention is embodied.

Fig. 2 is a section on the line 2-2 of Fig. 1.

Figs. 3 and 4 are both sections on the line 33 of Fig. 2, with the parts in difierent position.

As stated previously, what is shown herein is a four outlet carburetor, Fig. 1 showing the outline of a carburetor such as shown in full in the patent of Olson et al., Patent Number 2,771,282. The specific construction of the carburetor is entirely immaterial so far as the present invention is concerned so that no structural details of the carburetor are shown herein. Also, as already indicated, the invention is equally applicable to a dual carburetor having one primary and one secondary mixture passage as it is to the four outlet type.

As shown, the carburetor has three separate castings superposed on each other and separated by suitable gaskets and suitably secured together. These castings are the throttle body casting 2 in which the throttle valves which control the supply of combustible mixture to the engine are positioned, and which is secured in the conventional way to the inlet of the intake manifold. A fuel chamber in which fuel is maintained at a constant level is formed in the casting 4 as well as suitable passages for conveying fuel to the mixture passages which extend through the castings 4 and 2. The top casting 6 forms a cover for the fuel chamber and at its upper end has an opening which serves as an air inlet for supplying air to all of the mixture passages, both primary and secondary. There are two primary mixture passages 8 and two secondary mixture passages 10, one of each being shown in Fig. l.

In the throttle body casting 2 a primary throttle shaft 12 is rotatably mounted and secured to this shaft are two primary throttle valves 14 of identical construction, one of which is shown in Fig. 1. Each of these valves controls the flow of combustible mixture from one of the primary mixture passages and the shaft 12 is operated by a suitable operating connectionextending from such 3 shaft to the conventional accelerator pedal. Also, in the casting 2, there is rotatably mounted, a secondary throttle shaft.16 on which are secured two secondary throttle valves 18 which control the flow of combustible mixture from the secondary mixture passages to the engine. The shaft 16 is operated from the shaft 12 through a lost motion connection so that the primary throttles make a predetermined opening movement, for example, 40 before the secondary throttles start to open. A suitable form of operating connection is shown in the above mentioned pending application of Olson et al.

The means for conveying fuel from the fuel chamber to the several mixture passages is not shown in detail as its construction is wholly immaterial to the present invention. Sufiice it to say that a very rich mixture of fuel and air is supplied to the passage 20 and is delivered to the primary venturi tube 22 where it is mixed with additional air, and this primary mixture is discharged into the large venturi tube 24 which forms the main mixing chamber in each mixture passage. There it is mixed with sufiicient additional air, which is admitted through the air inlet in the top of the casting 6, to form a fuel-air mixture of properly combustible proportions. The means for conveying fuel from the fuel supply chamber to the several mixture passages is the same. No means for supplying fuel for idling operation of the engine is shown because such a means has nothing to do with the present invention, and such means could be of the construction shown in the aforementioned copending application if desired, or of any other suitable construction.

The flow of fuel mixture to the engine is controlled by the position of the throttles 14 and 18 to regulate the engine speed in the conventional manner and, as already set forth, if the throttles are opened from a slightly open position, such as they would occupy if the vehicle on which the device is used was proceeding at relatively low speed to a relatively wide open position, the secondary mixture passages would be rendered elfective. Air and fuel would flow into such passages, but the supply of air would increase faster than the fuel, and, hence, the airfuel mixture supplied would not be satisfactory. To prevent this action, the flow of air through each secondary mixture passage is retarded by a spring loaded, suctionoperated air valve positioned in such passage between the throttle and the large venturi tube 24, as shown in Figs. 1 and 2. The spring retarding forces effective on the suction-operated air valves are such that with varying engine load and wide open throttles, the suction operated valves will remain fully open within an optimum range of engine speed.

The secondary mixture passages 10 are enlarged at the upper face of the throttle body casting 2, as indicated at 26, so that the diameter of each passage is greater at this point and also the casting between the two mixture passages is cut away to form a recess of more or less elliptical shape, as indicated by the line 28 in Fig. 2. An insert 30 of the same peripheral shape as the recess is positioned therein. This insert fits tightly in the recess and seats on the shoulder 32, as indicated in Fig. 1. The insert has two openings 33 and 34 of the same size as the lower part of the mixture passage 10 and in these openings two suction-operated valves 36 and 38 are positioned. These valves are not flat butterfly valves of the ordinary type, but have the offset shape shown in Fig. 1. The design of these valves is not novel, but valves of the same shape are shown in the copending application of Elmer Olson SN 414,763, filed March 8, 1954 and are provided herein for the same purpose. Flat valves have a tendency to hang as they approach open position and this tendency is eliminated by the use of valves of the type disclosed.

The valves 36 and 38 are secured to a common shaft 40 which is suitably journaled for rotation in the insert 30, so that the valves move in unison in response to variations in suction elfective on such valves. As shown in Fig. 2, the insert 30 has a slot 42 formed in the right side thereof. Extending into this slot is a pin 44 which is secured to and extends from the shaft 40. Also extending across the slot 42 and rotatably received in a bore formed in the insert 30 is a pin 46. A pin 48 is screwed into the pin 46, as seen in Fig. 2, and this pin 48 is received in a bore 50 formed in the insert so that the pin 46 can not oscillate as the valve shaft 40 moves in respone to suction variations, and the pin 48 also prevents axial displacement of the pin 46 in the bore in which it is positioned.

A spring 52 is coiled around that portion of pin 46 which lies within the slot 42 and one end of the spring is secured to such pin. The other end of the spring 52 extends into the slot 42 and is bent in the form indicated so that a loop 54 at the extreme end of the spring 52 surrounds the pin 44. As will be apparent from Figs. 3 and 4, which show the parts in the closed and open positions, respectively, of the suction-operated valves, the loop slides on the pin 44 and moves toward the axis of the valve shaft 40 as the valves 36 and 38 move from closed toward open position. Obviously, the length of the lever arm, which is the pin 44, through which the spring 52 exerts a force in opposition to the force of engine suction tending to open valves 36 and 38 decreases as the valves are moved toward open position. As a result the effective force of the spring decreases. Since the effective suction force exerted decreases as the valves 36 and 38 open, the decreasing resistance to opening is highly advantageous since it permits rapid full opening movement of the suction-operated valves. In addition, the suctionoperated auxiliary valves will remain wide open over an optimum range of engine speed due to varying engine load when the primary and secondary throttle valves are wide open.

Obviously, although there are two secondary mixture passages and two valves 36 and 38 shown, this invention is equally applicable to a single suction operated valve in the single secondary mixture passage of a dual carburetor.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In a charge forming device for internal combustion engines having primary and secondary mixture passages to which fuel and air are supplied to form a properly combustible mixture therein, primary and secondary throttles in said primary and secondary passages respectively, said throttles being movable to different positions to variably control the quantity of mixure supplied to the engine, a suction operated valve in the secondary mixture passage movable toward open position on opening movements of the secondary throttle, a spring opposing the opening movement of said valve in response to an increase in suction elfective thereon, a lever arm connected to said valve through which the force of said spring is communicated to said valve, and means including a sliding connection between said lever arm and said spring for reducing the effective length of said lever arm as the valve is moved toward open position whereby the force exerted by said spring in opposing the movement of said valve is reduced as the valve is opened.

2. In a charge forming device for internal combustion engines having primary and secondary mixture passages to which fuel and air are supplied to form a properly combustible mixture therein, primary and secondary throttles in said primary and secondary passages respectively, said throttles being movable to diiferent positions to variably control the quantity of mixture supplied to the engine, a suction operated valve in the secondary mixture passage movable toward open position on opening movements of the secondary throttle, a rotatable shaft on which said valve is mounted, a pin extending from said shaft, a spring engaging said pin and tending to hold the valve in closed position, whereby the opening of said valve in response to an increase in suction is opposed by said spring in order to retard the opening of the valve, said spring being movable along said pin toward the valve shaft as the valve is opened in order to reduce the force exerted by said spring in opposition to the opening of the valve as the valve is moved toward open position.

3. In a charge forming device for internal combustion engines having primary and secondary mixture passages to which fuel and air are supplied to form a properly combustible mixture therein, primary and secondary throttles in said primary and secondary passages respectively, said throttles being movable to different positions to variably control the quantity of mixture supplied to the engine, a suction operated valve in the secondary mixurc passage movable toward open position on opening move ments of the secondary throttle, a rotatable shaft on which said valve is mounted, a pin extending from said shaft, a spring tending to hold the valve closed and having a loop formed at one end which surrounds said pin and is slidable thereon, said loop being movable along said pin toward the axis of the valve shaft as the valve is opened, whereby the length of the lever arm through which the force of said spring is communicated to the valve is reduced as the valve is moved toward open position.

4. In a charge forming device for internal combustion engines having two primary and two secondary mixture passages to all of which fuel and air are supplied to form a properly combustible mixture therein, primary and secondary throttles in said primary and secondary passages respectively, said throttles being movable to different positions to variably control the quantity of mixture supplied to the engine, a suction operated valve in each of said secondary passages movable toward open position on opening movements of said secondary throttles, a common shaft supporting both of said suction operated valves, a pin secured to said shaft and extending therefrom in a direction normal to the axis thereof, a spring having one end engaging said pin and slidable on said pin, said spring being effective to oppose rotation of said shaft as the latter is rotated upon opening movement of said valves, and the end of said spring being movable on said pin toward said shaft as the valves are opened, whereby the force of the spring opposing opening of the valves is reduced as the valves are moved toward open position.

5. In a charge forming device for internal combustion engines having two primary and two secondary mixture passages to all of which fuel and air are supplied to form a properly combustible mixture therein, primary and secondary throttles in said primary and secondary passages respectively, said throttles being movable to different positions to variably control the quantity of mixture supplied to the engine, a suction operated valve in each of said secondary passages movable toward open position on opening movements of said secondary throttles, a common shaft supprting both of said suction operated valves, a pin secured to said shaft at a point between the suction operated valves and extending from the shaft in a direction normal to its axis, a spring having one end engaging said pin and slidable on said pin, said spring being effective to oppose rotation of said shaft as the latter is rotated upon opening movement of said valves, and the end of said spring being movable on said pin toward said shaft as the valves are opened, whereby the force of the spring opposing opening of the valves is reduced as the valves are moved toward open position.

6. In a charge forming device for internal combustion engines having two primary and two secondary mixture passages to all of which fuel and air are supplied to form a properly combustible mixture therein, primary and secondary throttles in said primary and secondary passages respectively, said throttles being movable to different positions to variably control the quantity of mixture supplied to the engine, a carburetor housing through which all of said mixture passages extend, said secondary mixture passages being enlarged at a point anterior to the secondary throttles to form a recess, an insert positioned in said recess and having passages therethrough in alignment with the secondary mixture passages, a shaft rotatably mounted in said insert and extending across the passages, suction operated valves in such passages and secured to said shaft, a slot at one side of said insert, a pin extending from said shaft in a direction normal to the axis thereof and into said slot, a spring exerting a force to hold the suction operated valevs closed and positioned in said slot, said spring having one end slidably connected to said pin and movable along said pin toward the axis of said shaft as the valves secured to said shaft are opened, whereby the length of the lever arm through which the force of the spring is communicated is reduced as the suction operated valves are moved toward open position.

7. A charge forming device as described in claim 1 in which said spring is a torsion spring having a relatively non-flexing portion forming a part of the sliding connection between said lever arm and said spring.

References Cited in the file of this patent UNITED STATES PATENTS 2,434,192 Braun Jan. 6, 1948 2,438,734 Zimmerman Mar. 30, 1948 2,703,229 Henning Mar. 1, 1955 2,752,131 Gretz June 26, 1956 

